Lead/sulphuric acid accumulators (in the following referred to by the shorter term lead accumulator) contain to an ever increasing extent separators made from filled microporous polyolefins. These separators are microporous separators, the composition and manufacture of which is known from prior art (see example, DE-PS 1 267 423, DE-PS 1 298 712, DE-AS 1 496 123, DE-OS 35 45 615, DE-PS 35 40 718 and DE-PS 36 17 318).
In contrast to separators based on impregnated cellulosic paper, PVC or phenol-formaldehyde-resins, separators made from filled polyolefins offer various advantages. On the one hand by their favorable property characteristics separators made from filled polyolefins, for example, have a very low electrical resistance, very small pores, a low acid displacement and a high oxidation stability, the life duration and capacity of lead accumulators can be improved, and on the other hand there are also advantages in the manufacture of the accumulator. The high flexibility of the separators made from filled microporous polyolefins allows fully automatic enveloping of lead plates and final sealing of the side edges, with the result that the lead plates are protected in a separator pocket, closed on three sides.
However, in the use of separators made from filled polyolefins in lead accumulators undesired processes are also observed.
By the interaction of the applied current, constituents of the lead plates, of the battery acid and constituents of the filled polyolefin separators, intensely coloured substances mixtures are formed, which are not soluble in the battery acid. As a result of their low specific weight they rise to the surface of the battery acid and there cluster together to form intensely coloured, mostly dark and often adhesive agglomerates, which tend to be deposited on the contact surfaces between the accumulator acid and the accumulator constituents, for example on the housing. In the charging process, gases, which are released, rise as bubbles in the acid, bursting on the surface of the acid and thereby throwing acid and deposits upwards, which results in the lid, the lid opening, the lid closure possibly placed on it, and also possibly the level indicator and the outside of the accumulator housing being the covered with the deposits.
Deposits on the outside of the accumulator housing must be removed by an additional cleaning stage.
Housing for lead accumulators consist, for example, of polypropylene acrylic, polystyrene or glass and are therefore transparent or totally clear. When in use coloured, mostly dark deposits arising in the lead accumulator deposit themselves on the inside of the containers and are therefore visible from the outside. As the deposits themselves are not transparent, an exact assessment of the acid condition is prevented, thereby making the regular inspection and adjustment of the acid condition more difficult. Therefore, if enough water is not added, the concentration of the accumulator acid increases. At the same time the acid level in the accumulator can possibly sink so far, that the lead plates partly protrude out of the acid and dry out. Lead accumulators which for example are used for motor vehicles, are often fitted with a valve system for automatic water-addition. These lead accumulators are regularly attached to a water reserve tank via the valve system. In proper working order the valve system ensures that a certain level of liquid is maintained in the lead accumulator. However, if this type of lead accumulator contains separators made of filled polyolefins, then as described above, during the use of this lead accumulator, coloured, mostly dark substances are released which agglomerate. These often adhesive agglomerates deposit themselves on the floats and other parts of the valve system for water addition, sticking these together and making them incapable of functioning. Consequently no water is added, and the acid level in the accumulator decreases seriously.
Many lead accumulators are fitted with gassing openings made from porous materials, which facilitate an unhindered escape of the gases formed, but which however hold back liquid constituents and protect the accumulator from sparks or flames. If this type of lead accumulator contains the filled polyolefin accumulators described above, when the lead accumulator is in use, as described, there arises a formation of coloured, mostly dark and often adhesive deposits, which reduce the size of the degassing openings.